A simple, selective, and sensitive kinetic spectrophotometric method is described for the determination of trace amounts of phenylhydrazine, which is based on its inhibition effect oil the reaction between meta cresol purple (MCP) and periodate in the presence of bromide ions. The reaction was monitored spectrophotometrically by measuring the change in absorbance of MCP at 525 rim. The calibration graph was linear in the range of 1.0-10.0 mu M. The detection limit (3 sigma) was 0.020 mu M. The relative standard deviations for 10 replicate measurements of 3.0, 5.0 and 7.0 mu M of phenylhydrazine were 2.0%. 1.4%, and 0.90%, respectively. The potential interfering substances were studied in the presence of phenylhydrazine. The proposed method was applied to the analysis of water samples. (C) 2008 Elsevier B.V. All rights reserved.